It is known to store a digital image in the form of a bit map. Each bit represents the display value of a picture element (pixel) of the image. For example, each bit may indicate whether the corresponding pixel is black or white.
It is sometimes necessary to rotate such an image through 90.degree., either clockwise or counter-clockwise. For example, if an image is stored in "portrait" format (i.e. with its height greater than its width), it may be desired to rotate the image to allow it to be displayed on a screen with "landscape" format (i.e. with its width greater than its height).
Such a rotation can be performed purely by software means, by reading out each pixel value in turn and writing it into the appropriate locatin of the rotated image. However, this is a relatively slow process, since it requires each pixel to be handled seperately.
The object of the present invention is to provide a hardware rotation circuit which can assist such a rotation operation and hence allows it to be performed more rapidly.